Chlorine dioxide, an indirect food additive, has been found to be especially useful as a disinfectant, antiseptic and sanitizer. It is widely used to disinfect drinking water and various water supplies. In addition, chlorine dioxide finds use as a bleaching agent for flour, fats, textiles and as an antiseptic.
Although it has great beneficial chararacteristics, chlorine dioxide can not be transported commercially as a concentrated gas for its use and instead has been generated at the site where it is used.
Chlorine dioxide has shown great utility as an antiseptic for treating metal substrates such as dental and medical instruments and devices. However, the prior art methods for generating chlorine dioxide suffer from the disadvantage that large quantities of chlorite remain as a residue. Chlorite residues on food handling equipment and medical and dental surfaces that are to come in contact with humans are to be avoided or substantially minimized according to FDA and EPA regulations.
Separately, chlorine dioxide exhibits certain corrosive properties which are believed to be pH related. Thus, in certain applications, it is beneficial to generate chlorine dioxide at a pH which would avoid or minimize corrosion during the disinfecting process.
The production of ClO.sub.2 solutions is well known in the art. The general prior art procedure has been to mix sodium chlorite (NaClO.sub.2) with an acid. As a rule, the stronger the acid, the faster and more efficient will be the production of chlorine dioxide. The general formula for the production of chlorine dioxide using sodium bisulfate is as follows: EQU HNaSO.sub.4 .revreaction.Na.sup.+ +SO.sub.4.sup.-- +H.sup.+ (sodium bisulfate ionization) (1) EQU NaClO.sub.2 +H.sup.+ .revreaction.HClO.sub.2 (sodium chlorite acidification to chlorous acid) (2) EQU 5HClO.sub.2 .fwdarw.4ClO.sub.2 +2H.sub.2 O+Cl.sup.- +H.sup.+ (chlorous acid disproportionation to yield chlorine dioxide) (3) EQU 4HClO.sub.2 .rarw.2ClO.sub.2 +H.sub.2 O+Cl.sup.- +ClO.sub.3.sup.- +2H.sup.+( 4)
According to the reaction, the hydrogen ion concentration produced is much greater using a relatively strong acid, as opposed to a weaker acid (having a lower pKa). This increased hydrogen ion concentration will produce optimal concentrations of chlorous acid. Thus, lower concentrations of strong acids are needed to generate the same concentration of chlorous acid as are produced using weaker acids.
The prior art methods for generating chlorine dioxide result in large residues of chlorite ion. This can be a disadvantage where one wishes to minimize the residual chlorite ion, expecially when disinfecting or cleaning sensitive machinery or equipment. Thus, when the prior art solution is evaporated from the surface of food equipment, for example, the chlorite ion either in protonated form or as the conjugate base (depending upon pH) remains as unwanted residue.
Another requirement in the food handling and related industries is the need for raw materials or ingredients which are safe to handle in the preparation of the disinfectant. Strong acids such as nitric or hydrochloric may be dangerous to the unskilled personnel in the food handling unit and inappropriate for generating chlorine dioxide in this case. The requirement is for the inclusion of reagents which are safe to use and, after generating chlorine dioxide, produce side products which are non-toxic and/or biodegradable.
Although a number of attempts have been made in the art to enhance the efficiency of chlorine dioxide production and minimize the amount of residual chlorite ion, the results have generally been unimpressive. To date, there has been no report of the use of a hydroxyl free aldehyde to enhance the production of chlorine dioxide from an acid and a salt of chlorite.